I've had all kind of problems with Flip4Mac and SL. I tried the latest official release and also the latest beta which is supposed to be updated for SL and both have problems, particularly with streaming video. If I try to watch a video in Safari it opens in a tab and is audio only (despite my setting preferences to open in the media player). When trying to watch the same video in FireFox, it opens an infinite amount of tabs (continually opening new ones until I hit escape), but the video never plays.
I uninstalled, reinstalled, and click "relcaim file assosciations"... then it started trying to open videos in RealPlayer instead of Quicktime! Like you, it claims Quicktime is not installed.
Do you have QT 7 located in your applications/utilities folder? I think maybe two versions of QT may be confusing it.